ul 1008 ats withstand and close on ratings€“describe the ul 1008 requirements for transfer...
TRANSCRIPT
UL 1008 ATS Withstand and Close On Ratings
Revised: September 25, 2017
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Meet your panelists
Rich Scroggins
Technical Advisor, Field Support and Application
Engineering Group
Cummins
Cummins presenter:
Your local Cummins contacts:
AZ, ID, NM, NV: Carl Knapp ([email protected]), Rocky Mountain Region
CO, MT, ND, UT, WY: Joe Pekarek ([email protected]), Rocky Mountain Region
IL, IA, NB, SD: John Kilinskis ([email protected]), Central Region
WI, MN, ND: Michael Munson ([email protected]), Central Region
MO, KS: Earnest Glaser ([email protected]), Central Region
TX: Scott Thomas ([email protected]), Gulf Region
FL, GA, SC, NC and Eastern TN: Robert Kelly ([email protected]), South Region
IN, KY, OH, TN, WV: Thomas Stadulis ([email protected]), East Region
NY, NJ, CT, PA, MD: Charles Attisani ([email protected] ): East Region
CA, HI: Brian E Pumphrey ([email protected])
WA, OR, AK: Tom Tomlinson ([email protected])
For other states and territories, email [email protected] or visit http://power.cummins.com/sales-service-locator
Cummins facilitator:
Tom Bakritzes,
Global Sales Training Manager
Cummins
Objectives
Participants will be able to:
–Describe the UL 1008 requirements for transfer switch
short circuit withstand and closing ratings
–Specify withstand and closing ratings to allow for
transfer switch selection and system design.
UL 1008 Short Circuit Ratings
UL 1008 requires all ATS to have a withstand
and closing rating (WCR)
Rating can either be time based or specific
OCPD (Breaker) based
Specific breaker based ratings allow for
higher available fault current but requires the
ATS to be protected by a listed breaker
UL changed the requirements for listing
breakers which has reduced the number of
listed breakers for all ATS manufacturers
Many commonly used breakers remain
Allowing for either time based or specific
breaker based ratings enables flexibility for a
cost effective design
Short Circuit Testing (UL 1008)
Transfer switches must have a WCR rating
The WCR rating may be based on either:
– A specific duration
– A specific overcurrent protective device
Test sequence is as follows:
– Specified fault current is applied for either
• A specified period of time (e.g. 50 ms)
• Until the specified overcurrent protective
device clears the fault
– After withstanding the fault current, the ATS
must close into the fault using the same set of
contacts
Short Circuit Testing (UL 1008) Specific Duration Test
– ATS must withstand specified current
applied for a specific duration
• Allowed durations range from 8 ms
(1/2 cycle) to 100 ms (6 cycles)
– After withstanding the fault current, the
ATS must close into the fault using the
same set of contacts
– Maximum short circuit current, voltage
and short circuit duration must appear
on the label
Short Circuit Testing (UL 1008)
Specific overcurrent protective device test
– ATS must withstand specified current
applied until overcurrent protective
device clears
– After withstanding the fault current, the
ATS must close into the fault using the
same set of contacts
– Rated devices along with the maximum
current and voltage must be declared on
product markings or documentation
What is an any breaker rating?
“Any breaker rating” has never been a recognized term by UL
“Any breaker rating” is commonly used for a 50 msec or 3 cycle time
based rating
Comes from the UL 489 requirement that Molded Case Circuit
breakers rated 400 amps and above must clear a fault in no more
than 50 msec (3 cycles)
– Fault clearing time requirement for molded case breakers rated
less than 400 amps is 25 msec
Applying the “any breaker rating” when the breaker is not listed to UL
489 is a code violation
WCR Test: Specific Duration
Acceptance Criteria
– Operable by intended means
– No Breakage of Switch Base
– Door Must Be Secure
– No Conductors Pulled Out of Terminals
– Must Pass Dielectric Test
Switch is not required to carry rated current after the test, or even work
400A Switch tested at:
480VAC, 35k Amps, 50ms
WCR Test: Specific Duration
400A Switch tested at:
480VAC, 35k Amps, 50ms
Short Circuit Testing (UL 1008)
Transfer switches may also have a Short Time Rating of up to 0.5 sec
(30 cycles)
– Same test as a specific duration test except switch must pass a temperature rise
test after the short circuit
– Demonstrates that the switch can still carry rated current
– Maximum short circuit current, voltage and short circuit duration must appear on the
label
The WCR is considered a safety rating
The short time rating is considered a performance rating
UL 1008 Change
Before UL1008 7th edition, a new breaker could
be added by comparing the max published trip
time with the max published trip time of the
tested breaker
MAX published trip time of new breaker ≤
MAX published trip time of tested breaker
After UL1008 7th edition, a new breaker can be
added by comparing the max published trip time
with the tested trip time using the original
breaker
MAX published trip time of new breaker ≤
ACTUAL tested breaker trip time measured
during the UL witness test
Effectively most circuit breakers must be tested
in order to be added to the specific breaker list
Current
Tim
e
New
Breaker
Tested Breaker:
Max Published Trip Time
Tested Breaker:
Actual Trip Time
WCR with commonly used breakers
Commonly used circuit breakers from Square D, GE,
Siemens and Eaton are listed for Cummins ATS under UL
1008 7th Edition
ATS Short Circuit Ratings
Several Short Circuit Ratings are available at each amp node
Specific overcurrent device ratings are substantially higher than time
based ratings
– As high as 200,000 amps with current limiting breakers and fuses
Max Fuse, Size and type
480 600 240 480 600 240 480 600 240 480 600
OTEC, OTPC BTPC
600 A Class J, RK1, RK5 or
1200 A Class L, T 200,000 200,000 125,000 100,000 50,000 200,000 200,000 200,000
OHPC, CHPC
400 A Class J or T or 200 A
Class RK1 or 100 A ClassrK5 200,000 200,000 200,000 200,000 200,000 0.050 25,000 25,000 18,000 0.167 25,000
OTEC, OTPC BTPC
600 A Class J, RK1, RK 5 or
1200 A Class L, T 200,000 200,000 125,000 100,000 50,000 200,000 200,000 200,000 0.050 25,000 25,000 25,000
OHPC, CHPC
400 A Class J or T or 200 A
Class RK1 or 100 A ClassrK5 200,000 200,000 125,000 100,000 50,000 200,000 200,000 200,000 0.050 35,000 35,000 22,000 0.500 30,000
WCR @
480V
260
300
Time Based Ratings Short Time Ratings
WCR @ Volts WCR @ Volts WCR @ Volts Time
(sec)
WCR @ Volts Time
(sec)Amps ATS Model
Bypass
Model
Fuse protection
Specif ic Breaker Protection
(Common)
Specif ic Breaker Protection
(General)
Spec Recommendations
ATS Specs are usually written based on incomplete information
– Circuit Breakers have not yet been selected when the spec is written
– In some cases available fault current is not known
• 20X the service rating is a reasonable estimate
• Assumes transformer with 5% impedance
Spec language should allow ATS supplier to meet the requirement with
either a specific device rating or a specific duration rating
Allows for flexibility in selecting ATS once breakers are selected
Opportunities to use a smaller, less expensive ATS if selected breaker is
listed for the ATS
Recommended language from AIA Spec
Tested Fault-Current Closing and Short-Circuit Ratings: Adequate for
duty imposed by protective devices at installation locations in Project
under the fault conditions indicated, based on testing according to
UL 1008.
ATS can comply with either time based or specific breaker based
rating
Ratings based on a specific overcurrent device will be significantly
higher than a specific duration rating
The higher rating often allows use of a smaller, less expensive
transfer switch
ATS suppliers will help identify listed breakers
Conclusions
Most transfer switches have several short circuit Withstand and Close On ratings
based on fault duration times and on specific overcurrent protection devices.
Specific overcurrent device ratings are almost always higher than time based ratings
– This allows for the smallest most cost effective transfer switch to be selected when
these ratings can be applied.
Specifications should require that the transfer switch short circuit ratings be
coordinated with the overcurrent protective devices at the fault current available on
the line side of the transfer switch.
– Allows for flexibility in selecting transfer switches once breakers are chosen for the
project
– Minimizes the possibility of having to oversize the transfer switch to meet the short
circuit WCR requirements.
Work with your Cummins distributor for assistance in selecting transfer switches for
your application
Q&A
Type your questions, comments, feedback in the WebEx
Q&A box. We will get to as many questions as we can
We will publish consolidated FAQ along with presentation
and webinar recording on powersuite.cummins.com
Your local Cummins contacts:
AZ, ID, NM, NV: Carl Knapp ([email protected]), Rocky Mountain Region
CO, MT, ND, UT, WY: Joe Pekarek ([email protected]), Rocky Mountain Region
IL, IA, NB, SD: John Kilinskis ([email protected]), Central Region
WI, MN, ND: Michael Munson ([email protected]), Central Region
MO, KS: Earnest Glaser ([email protected]), Central Region
TX: Scott Thomas ([email protected]), Gulf Region
FL, GA, SC, NC and Eastern TN: Robert Kelly ([email protected]), South Region
IN, KY, OH, TN, WV: Thomas Stadulis ([email protected]), East Region
NY, NJ, CT, PA, MD: Charles Attisani ([email protected] ): East Region
CA, HI: Brian E Pumphrey ([email protected])
WA, OR, AK: Tom Tomlinson ([email protected])
For other states and territories, email [email protected] or visit http://power.cummins.com/sales-service-locator
Closing
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